1. Field of the Invention
The present invention relates to an optical fiber type vibration meter having a light source; an optical fiber guiding light from the light source, a vibration probe to which the guided light is made incident; an optical receiver photoelectric-converting light modulated by vibration of a movable member arranged in the vibration probe to output the light as an electrical signal; and a processor processing the electrical signal to output a state of the vibration as an output voltage value. In particular, the present invention relates to an optical fiber type vibration meter capable of high precision measurement.
2. Description of Related Art
Conventionally, there are various types of vibration meters. For example, the vibration meters can be divided into a group of an optical fiber type and a group of a non-optical fiber type. In a vibration meter of a non-optical fiber type, as disclosed in Publication 1, output from a vibration probe is an electrical signal. Therefore, when a cable from the vibration probe is long, it is susceptible to electromagnetic induction noises. At the same time, transmission loss via a cable cannot be ignored, and it is possible that signal quality may deteriorate.
On the other hand, a vibration meter of an optical fiber type outputs light from a vibration probe using an optical fiber as a transmission path (for example, Related Art 1). Therefore, a vibration meter of an optical fiber type has an advantage in that, even when the optical fiber cable is long, there is nearly no deterioration in signal quality, and high explosion proof can be maintained without being affected by electromagnetic induction noises.
[Related Art 1] Japanese Patent No. HEI 3-22595 B2.
[Publication 1] Mitutoyo, Vibration Pickup, Catalog No. 4351.
However, the optical fiber type vibration meter disclosed in Related Art 1 obtains an acceleration output by assuming that a displacement of a weight (a movable member) in a seismic system is proportional to vibration acceleration. Therefore, in Related Art 1, the acceleration output is affected by static gravity, and an offset error occurs.
As solutions to this problem, passing an acceleration output through a high-pass filter, removing an average value of data, electrically zero-setting an acceleration output, and the like, have been considered. However, for the former two, when it is an asymmetric vibration or when an average data length is not an integral multiple of a vibration wavelength, an error remains. For the latter, there is a problem that it is not applicable in a situation where a state of zero vibration cannot be ensured. Further, in order to perform these processes, there is a possibility that a processor processing a signal from a vibration probe becomes complex.